It seems to me to make the best use of power in the narrow power band that we have with these engines. Same reason I dont get people running 3500+ rpm convertors when thats right about where the engines out of steam any way. It makes since to me to utilize the advatanges of the diesel by design....... low speed torque.
Diesels actually have a pretty wide powerband in comparison to most gassers. Looking at a dyno sheet I have laying on my desk I see at least 500rwhp from ~2500rpm to ~3800rpm. So it made 500+ over a range of 1300rpm. You look at that and intuitively it might seem like a narrow range. But it's actually a change in rpm of 1.52:1. Which is all that matters in terms of
Powerband. And is subsequently why a comparably powered diesel will usually outrun a gasser even when the dyno sheets look similar.
For instance, take a gasser that makes at least 500hp from say 5000rpm to 7000rpm. It is clearly making 500hp or more over a range of 2000rpm. That might lead you to believe it has a broader powerband, but that would be incorrect. Because while it makes the power over a range of 2000rpm, the problem is this only represents an rpm change of 1.4:1. Meaning it literally only spun the input shaft 1.4 times faster at 7000rpm as it did at 5000rpm. So truth be told, the diesel above actually has an 8.5%
wider powerband than the gasser.
Which explains why a diesel equipped model will almost certainly outrun/outpull a gasser equipped model of comparable power day in and day out.
If that seems off, or doesn't ring true, let me try to explain in another way:
Say you have a situation where you are accelerating the vehicle with each of these two engines one at a time. Say it's from a roll, and at the speed you're starting at each time the output shaft speed of the trans is 2500rpm. Okay, simple enough.
So take the gasser. If we set up a trans where the engine will start the pull at 5000rpm (so it's in it's powerband) it will need a trans ratio of ~2:1. Which is about second gear on a ZF6. We'll just say the ZF6 is exactly 2.0:1 in second since it's actually like 2.1 or so. Alright, so the gasser is in second gear turning 5000rpm with the output shaft spinning 2500 and he nails it. It's making 500+hp and accelerating up to 7000rpm where the output shaft is now spinning 3500rpm. So out of that 2000rpm powerband you got an actual output shaft rpm range of 1000rpm in a real-life scenario.
So take the diesel. Since its powerband starts at 2500rpm it will make the pull in 3rd gear which is 1:1. So it starts at 2500rpm with an output shaft rpm of 2500 and then you nail it and it makes 500hp while accelerating up to 3800rpm where the output shaft is then spinning 3800rpm. Whoa..... the output shaft is turning 300rpm faster even though the engine only accelerated over a range of 1300rpm vs the 2000 for the gasser. Correct.... however, as you see from above, that is a change of 1.52:1 vs 1.40:1 for the gasser.
3800 vs 3500?
Yep, it's the same 8.5% more that we noted above. This is the "magic" behind diesels. And why they actually have a broad powerband even though they don't operate over a broad rpm range. This is because the percentage change to the rpm for a diesel is large.